Hypoxia inducible factors 1 and 2 (HIF-1 and HIF-2) are heterodimers consisting of α and β subunits, and are transcription factors having a basic helix loop helix (bHLH) domain and a PAS domain in common. The expression and transcription activity of HIF markedly increase as the intracellular oxygen concentration decreases. As a target gene transactivated by HIF, VEGF (vascular endothelial cell growth factor), erythropoietin, glucose transporter, and a gene encoding enzyme of glycolysis and the like have been identified (see non-patent document 1).
Diabetic retinopathy and age-related macular degeneration are causative diseases resulting in acquired blindness, and the development of a medicament that suppresses angiogenesis found in the both diseases is currently desired. Particularly, an intraocular increase of VEGF is known to be one of the causes of angiogenesis induction, and some VEGF antagonists are under development. HIF is a transcription factor that controls expression of VEGF, and an HIF inhibitor is also expected as an angiogenesis suppressing agent.
Studies using siRNA as an HIF inhibitor have reported that expression of VEGF is suppressed by HIF-1α siRNA in HeLa cells, Hep3B cells and Kelly cells (see non-patent document 2). In addition, it has also been reported that only HIF-1α siRNA suppresses induction of VEGF expression due to hypoxia in breast cancer cells (MDA468), and suppression does not occur by HIF-2α siRNA (see non-patent document 3). Even when siRNAs for the both isoforms of HIF-1α and 2α were used in this experiment system, the induction of VEGF expression was suppressed only to the same level as the sole use of HIF-1α siRNA. In contrast, reports have documented that only HIF-2α siRNA suppresses induction of VEGF expression due to hypoxia in kidney cancer cells (786-O), and each siRNA for HIF-1α and 2α suppresses VEGF expression in kidney cancer cells (Caki-1) having tumor suppressor gene VHL (von Hippel-Lindau) (see non-patent document 4). As mentioned above, which isoform of HIF is deeply involved in VEGF production is considered to vary depending on the cell.
Heretofore, use of siRNA and antisense for HIF-1α as a therapeutic drug for age-related macular degeneration and diabetic retinopathy has been reported (see patent documents 1-3). However, use of siRNA and antisense for HIF-2α has not been reported as far as the present inventors know. In addition, it has not been reported that inhibition of both isoforms of HIF-1α and HIF-2α markedly enhances VEGF production suppressive action as compared to inhibition of one of the isoforms, nor is there reported use of a composition containing siRNA(s) or antisense(s) for both isoforms of HIF-1α and HIF-2α for retinal diseases.    patent document 1: WO2007/002718    patent document 2: WO2004/042024    patent document 3: WO2006/050734    non-patent document 1: Semenza GL (1999), Ann. Rev. Cell. Dev. Biol. 15: 551-578    non-patent document 2: Christina W et al (2004) FASEB J 12: 1462-1464    non-patent document 3: Heidi M S et al (2004) Cancer Res 63: 6130-6134    non-patent document 4: Raju RR et al (2005) Molecular and Cellular Biology 25: 5675-5686